First, a structure of a conventional electric blower is described below.
The conventional electric blower includes a stator, a rotor, a bracket, a rotary fan, an air guide, and a fan case.
The conventional electric blower converts dynamic pressure obtained by the centrifugal force of the rotary fan to static pressure by the air guide to generate air output.
The conventional electric blower is configured such that a large distance is secured between a rear rim (trailing edge) of the rotary fan and a front rim of a diffuser, so as to reduce noise.
Other structures have been proposed, including a structure to suppress pressure fluctuation when a rear rim of a rotary fan impeller crosses the front rim of the diffuser and a structure to reduce the number of revolutions of the rotary fan.
In addition, to reduce resonance inside a flow passage, a structure is proposed to suppress resonance and reduce impeller sound by providing a through hole at a position where a wave node exists. (e.g., PTL 1)
In the conventional air blower as configured above, airflow slip at the rear rim of impeller or backflow increases if a distance between the rear rim of the rotary fan and the front rim of the diffuser becomes long. This increases pressure loss.
Dynamic pressure generated by the rotary fan reduces if the number of revolutions reduces in the conventional electric blower. As a result, the air-blow efficiency reduces.
Furthermore, a through hole is provided at a position where a wave node of resonance exists in PTL 1. This reduces resonance in a flow passage. If the flow passage is short in this type of the conventional electric blower, the resonance node, which is a passage outlet, is positioned in a semi-open area. This significantly reduces the air-blow efficiency. In addition, assembly becomes difficult if a through hole is provided at a position where the wave node of resonance exists. The air blower cannot be manufactured using upper and lower dies. A separate horizontal die becomes necessary. If the diffuser and a partition plate are configured separately, assembly becomes difficult.    PTL1 Japanese Patent Unexamined Publication No. 2009-299636